This fossil appears to be the bottom of a
Lyriocrinus calyx cup found in the Waldron Shale of Clark County, Indiana. It is dated to the Middle Silurian Period (425-419 million years ago). The reason I identified it as
Lyriocrinus as I found another cup nearby. The most common crinoid cup found is the
Eucalyptocrinus which is this layer's index fossil. Fossil is about 3 cm wide.
